Anode problems

Solitaire

Solitaire

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I'm having very bad anode corrosion. I have heard that this can be (partialy) overcome by hanging a lump of zinc over the stern attached by a wire. Can any member(s) give me more details on how to do this please?

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As far as I know the anode which you hang over the side must be put in circuit with the boat anode. The rate of loss on the two anodes will be directly proportional to their relative mass/size. Make sure both anodes are of the same metal ie Zinc for use in salt water.

Trevor

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You can buy over-the-side anodes on a wire, but as already stated, the inboard end of the wire MUST be attached to whatever you are protecting, or something with good electrical contact to it. In most cases, attaching to the engine block will work, assuming there is no insulating barrier between it and the prop. You can make up your own over-the-side anode by using bits of old anodes screwed firmly to a strip of metal with a wire attached. Protect where the wire goes over the side for chafing - acts like a chain saw.

Regarding rate of reaction, I believe this is inversely proportionate to the distance between the dissimilar metals. For example, an anode on the prop shaft close to the prop will work much harder than an anode hanging in water a meter away. However, the more anode area exposed (or more anodes), the slower the dissolution of them all.

I'm not an expert on this (and it's a bit of a black art anyway), but if you are having rapid dissolution of anodes, you may have some stray currents around. Are you connected to shore power? Do you have a wind generator going continuously? Are there neighbouring boats on shore power? In themselves, these are not problems PROVIDED there is no associated current leakage. I suggest before adding more anodes, you discover and fix what is causing the rapid loss. I am sure there are others more qualified to comment on this.

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I had serious anode problems Three outdrives / stainless props etc etc.

Problem went away with the installation of electric anodes



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What do you call bad? How large/what weight is the anode and over how long is the corrosion taking place, a season, a year or what?


Phil

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Where is your boat moored? Swinging mooring, Marina, etc.

Do you have shore power? If so there might be a problem with how the local supply is earthed, and the fact that boat earth is at a slightly different potential to supply earth.

Regards John

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Sounds like your outdrive leg is the reason for the fast anode wear.

You can hang a lump of zinc over the side on a large wire as long as it is in circuit with the other anode - mostly people ground them to an engine flywheel bolt - I'd check your engine is already bonded to the disappearing anode.

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Have only ever visited the Hamble, going West, so didn't know the area was well known for quick/rapid errosion. Has anyone had any analysis done of the water for other than normal constituatnts as 3 months is very rapid.

Living aboard, with shore power in use a lot of the time, and a whole host of gadgets protected by the anodes they last two years on Spains eastern coast, and didn't need replacing in the two years we were in Devon before leaving.


Phil

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If your anode is corroding, it is doing what it is supposed to be doing! It is protecting your prop from corroding. If corosion seems excessive then you have an electrical leak some where. Try to locate this fault.

anabel

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Our friends on the mooring next to ours were having trouble with anodes and props being eaten away within a matter of months. When the pontons were being replaced we watched the dredger with interest, as it got closer to the jetty it would scoop up more and more cabling. It looked like the original contractors would get to the end of the pontoon cut the cable to the length they wanted and chuck the rest into the marina.

In the next low tide get down there and have a poke about.
Trudie

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